The present invention relates to a brake booster for an automotive brake system with regenerative brake force generation, comprising: a force input element that may be or is coupled to a brake pedal, a chamber arrangement having a vacuum chamber and a working chamber that are separated from one another by a movable wall, a control valve, by means of which in accordance with a displacement of the force input element the working chamber is connectable selectively to the vacuum chamber and the atmosphere to generate and reduce a differential pressure at the movable wall, wherein the control valve has a control valve housing that is connected for joint movement to the movable wall.
For some time now brake boosters have been a component part of modern automotive brake systems. They are used to boost the brake force exerted by a driver on a brake pedal by means of a synthetically generated servo force in order to enable comfortable actuation of the braking system of the motor vehicle. In other words, a conventional brake booster ensures that a driver has to apply a lower actuating force to the brake pedal for actuating the brake system than would be the case without a brake booster. More recently, brake boosters have been used increasingly to activate the brake system independently of the driver. In this connection, in addition to the generic term “brake booster”, the term “brake force generator” is also frequently employed. Such a driver-independent actuation is required for example when drive assist systems carry out an activation of the brake system independently of the driver, for example in the event of hazardous situations or in the event of excessive or too weak actuation by the driver.
A conventional vacuum brake booster is known for example from the document DE 34 13 739 A1. In addition to the conventional booster function, in this prior art it is provided that the air flows, which arise in the brake booster during actuation and may have relatively high flow rates, are guided by means of individual vanes of an air guide element in a desired manner in order to prevent turbulence that may lead to undesirable noise generation.
Conventional brake boosters are used also in the hybrid vehicles that have recently become popular. Such vehicles are characterized by having, in addition to an internal combustion engine, a second alternative drive source, for example an electric motor that may simultaneously also be used regeneratively. In this case it is provided that the electric motor is used for example during braking of the vehicle as a generator, wherein the energy demand for this purpose brings about a deceleration of the motor vehicle. Experience has shown that in specific operating situations such a regenerative deceleration of the motor vehicle is in fact sufficient to cover the deceleration effect requested by the driver through an actuation of the brake pedal. In the case of more powerful braking operations, in particular emergency braking operations, however, this deceleration effect is far from being able to cover the requested deceleration demand. It is therefore necessary, in addition to the deceleration effect produced by the electric motor acting as a generator, also to enable a braking of the motor vehicle by means of a conventional braking system.
Conventional brake boosters, such as are described for example in the document DE 34 13 739 A1, do however have the drawback of responding immediately upon a brake pedal actuation. This is briefly explained with reference to the accompanying FIG. 6, which shows essential components of a conventional brake booster in a starting position. In this starting position of the brake booster a valve element 1 lies sealingly against a first sealing seat 2 of a control valve housing 3. A second sealing seat 4 of a transmission element 5, which is coupled for joint movement to a force input element 6, moreover likewise lies sealingly against the valve element 1. The first sealing seat 2 in the illustrated position separates a working chamber from a vacuum chamber. The second sealing seat 4 in the illustrated position separates the working chamber from the ambient atmosphere. If the force input element 6 is then moved as a result of a brake pedal actuation out of the position shown in FIG. 6, this leads directly to a separation of second sealing seat 4 and valve element 1 and hence to a fluidic connection between working chamber and ambient atmosphere. A pressure difference consequently builds up at a movable wall 7. In other words, the brake booster according to prior art responds immediately to a pedal actuation. This immediate response of the brake booster to a brake pedal actuation considerably complicates use of the brake booster in hybrid vehicles. In particular, with such brake boosters a coordination between the deceleration effect produced by the electric motor and the deceleration effect produced by the conventional braking system is difficult.